Directional coupler sensor

ABSTRACT

A directional coupler sensor is provided for measuring the moisture content of a substrate, such as hair. The sensor incorporates a high frequency directional coupler having a pair of generally parallel plates defining a coupling gap therebetween. A high frequency signal generator generates an electromagnetic field across the gap with the substrate placed across the coupling gap. The coupled power relates to the moisture content of the substrate. A pressure sensor is provided to ensure that the desired compactness of the substrate across the coupling gap is achieved to obtain accurate, reliable and consistent results.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/387,474, filed Jun. 10, 2002.

FIELD OF THE INVENTION

The present invention relates generally to measurement sensors and, moreparticularly, to a sensor for measuring a property of a substrate, suchas the internal and external moisture content of biological systems suchas hair.

BACKGROUND OF THE INVENTION

Human hair is made up of a complex protein called alpha-keratin. Proteinmolecules of the hair are arranged in organized patterns and are heldtogether by weak bonds, such as hydrogen, saline and hydrophobic bonds,and stronger ionic bonds and sulphur bridges. These bonds lend stiffnessor rigidity to the hair and enable styling of the hair with waves andcurls as these bonds are broken and then re-established in differentorientations through the styling process. As is known, styling of hairmay be accomplished by breaking the bonds by adding energy to the hair,such as by heat with a curling iron or blow dryer, or by getting thehair wet or damp. When the hair is wet or damp and the hydrogen bondsare broken, the hair becomes elastic and can be stretched and given aparticular form since the position of the keratin chains has beenaltered. As the hair dries, the bonds reform in different places,maintaining the hair in its new shape. Blow-drying or setting assists incontrolling the styling process so that, once dry, the hair will retainthe form it has been given.

Hair is hydroscopic and permeable so it will absorb water from theenvironment. Under normal conditions, water accounts for about 12% to15% of the composition of hair. Normal hair can absorb more than 30% ofits own weight in water. If the hair is damaged, this percentage canapproach 45%, however damaged hair has less ability to retain waterwithin the hair fibers which gives hair its healthy appearance. As morewater is absorbed within the hair fiber due to humidity or prior damage,the hydrogen bonds may loosen so that the hair has a decreased abilityto maintain its set.

During styling, if the hair is too wet, it will not hold its shape andwater must be removed before styling will be effective. Conversely, whenthe hair is too dry, the hydrogen bonds will have already been formedand poor styling will result since the keratin chains cannot berepositioned and set. It has previously been determined that optimumstyling results may be achieved when the moisture of hair is in therange of approximately 30-40% by weight. It is thus desirable to be ableto tell when to begin styling (i.e., when moisture in the hair is in arange of 30-40%) to obtain the optimum styling results.

Likewise, it is also important to know when to stop styling hair whichhas been wetted to break the hydrogen bonds. If the hair is too dry, itwill not be flexible and potential damage of the hair may result whenstyling is continued. It has been determined that the process of dryinghair exhibits two stages which are relevant to styling. In a primarydrying stage, water is evaporated from the outside of the hair fibersand no styling benefit is achieved. In a secondary drying stage, waterfrom inside the hair fibers is diffused to the environment. It is duringthis transition to the secondary drying stage when optimum styling ofhair may be achieved. A moisture level of about 30% is a balance betweenproviding enough water to disrupt the hydrogen bonds to allow the hairto shape and not enough water that must be removed for the hydrogenbonds to be reformed.

Moisture sensing devices have been developed in the past to determinethe moisture level in hair, and have relied on various techniquesincluding resistance and capacitance measurements to obtain the desiredindication. However, these methods only work well for a known crosssectional quantity and density of the hair being measured. As the hairdensity or compactness is varied, these measurement techniques fail.Additionally, these techniques rely primarily on the moisture contentoutside of the hair fiber for the measurement, and do not have theability to accurately measure moisture content within hair fibers aswell.

Thus, there is a need for a sensing device which can accurately andreliably determine the moisture content of a substrate, such as hair,including moisture both inside and outside of the hair fiber.

SUMMARY OF THE INVENTION

The present invention overcomes the foregoing and other shortcomings anddrawbacks of moisture sensors and methods of determining moisturecontent heretofore known. While the invention will be described inconnection with certain embodiments, it will be understood that theinvention is not limited to these embodiments. On the contrary, theinvention includes all alternatives, modifications and equivalents asmay be included within the spirit and scope of the present invention.

In accordance with the principles of the present invention a directionalcoupler sensor is provided for measuring the moisture content of asubstrate, such as hair. As the moisture content of a substrateincreases, so does its effective relative electrical impedance. Thesensor of the present invention is designed to measure the relativeimpedance of a substrate, and from that measurement, the moisturecontent of the substrate can be determined.

The sensor of the present invention incorporates a high frequencydirectional coupler having a pair of generally parallel strips thatdefine a coupling gap therebetween. A high frequency signal generator iselectrically coupled to one of the strips and generates anelectromagnetic field across the coupling gap to couple power to theother strip with the substrate placed across, i.e., generally normal tothe longitudinal axis of, the coupling gap. The signal generator ispreferably operable to generate signals in the VHF to UHF frequencyranges, although other frequency ranges are possible as well. The VHFfrequency range is between about 30 MHz and 300 MHz, and the UHFfrequency range is between about 300 MHz and about 3 GHz. The signalgenerator generates a coupled power signal in the coupled strip that hasan amplitude related to the impedance, and therefore the moisturecontent of the substrate placed across the coupling gap.

In accordance with another aspect of the present invention, a pressuresensor is provided to ensure a proper packing pressure of the substrateplaced across the coupling gap. The pressure sensor incorporates a filmtransducer in one embodiment that generates an output voltage signalthat varies with the packing pressure applied to the substrate placedacross the coupling gap. The measurement of the moisture content of thesubstrate is triggered upon the crossing of a pre-set pressurethreshold. This ensures that the desired compactness of the substrateplaced across the coupling gap is achieved to obtain accurate, reliableand consistent results. Alternatively, the packing consistency can beachieved by a mechanical system as well. The features and objectives ofthe present invention will become more readily apparent from thefollowing Detailed Description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the invention.

FIG. 1 is a functional block diagram of a directional coupler sensor inaccordance with the principles of the present invention;

FIG. 2A is a circuit representation of a high frequency signal generatorfor use in the sensor of FIG. 1 in accordance with one embodiment of thepresent invention;

FIG. 2B is a circuit representation of a directional coupler for use inthe sensor of FIG. 1 in accordance with one embodiment of the presentinvention;

FIG. 2C is a circuit representation of a moisture content detector foruse in the sensor of FIG. 1 in accordance with one embodiment of thepresent invention;

FIG. 2D is a circuit representation of a pressure sensor for use in thesensor of FIG. 1 in accordance with one embodiment of the presentinvention;

FIG. 2E is a circuit representation of a voltage regulator for use inthe sensor of FIG. 1 in accordance with one embodiment of the presentinvention;

FIG. 3 is a top plan view of the sensor of FIG. 1 shown integrated ontoa printed circuit board;

FIG. 3A is a cross-sectional view taken along line 3A-3A of FIG. 3;

FIG. 4 is a perspective view of a directional coupler sensor system inaccordance with one embodiment of the present invention;

FIG. 4A is an enlarged front elevational view of a hair clamping devicefor use in the sensor system of FIG. 4, illustrating the clamping devicein an open position to receive hair in the device;

FIG. 4B is a view similar to FIG. 4A, illustrating the clamping devicein a closed position to clamp hair in the device;

FIGS. 5A and 5B are side elevational views of a hair brush incorporatingthe directional coupler sensor of the present invention;

FIG. 6 is a graph illustrating the relationship between output voltageof the directional coupler sensor and relative humidity for variousswitches of hair;

FIG. 7 is a graph illustrating the relationship between moisture contentof hair by weight and relative humidity of hair; and

FIG. 8 is a graph illustrating the relationship between output voltageof the directional coupler sensor and pressure applied to pack the hair.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the Figures, and to FIGS. 1 and 2A-2E in particular, adirectional coupler sensor 10 is shown in accordance with the principlesof the present invention. For the sake of simplicity, the sensor 10 willbe described herein in connection with measuring the moisture content ofhair. However, it will be appreciated by those of ordinary skill in theart that the present invention has use in a wide variety of applicationsand is therefore not limited to the analysis of hair or the measurementof moisture content in a substrate. Rather, the sensor 10 of the presentinvention is readily adaptable to analyze a wide variety of substratesand to measure different moisture related properties of those substratesas will be readily appreciated by those of ordinary skill in the art.

For example, in the measurement of the moisture content of a substrate,the sensor 10 of the present invention operates under the principle thatas the moisture content of a substrate increases, so does its effectiverelative electrical impedance. As will be described in greater detailbelow, the sensor 10 is designed to measure the relative impedance of asubstrate, and from that measurement, the moisture content of thesubstrate can be determined. The moisture content value may be presentedon a visual display, indicated through a user-perceptible audible toneand/or used as a control signal to control a function of a device.

As shown in FIGS. 1, 2A-2E, 3 and 3A, the sensor 10 incorporates a highfrequency directional coupler 12 having a pair of generally parallelstrips 14 a and 14 b that define a coupling gap 16 therebetween. In oneembodiment of the present invention, the parallel strips 14 a, 14 b aresupported on an FR4 printed circuit board 18 (FIGS. 3 and 3A) having aground plane 20 formed on a lower surface of the board 18. In oneembodiment of the present invention, the height “h” of the PCB 18 is0.062 in., each strip 14 a, 14 b has a width “w” of 0.15 in. and alength “l” of 0.350 in., and the coupling gap 16 has a gap distance “s”of 0.020 in. Of course, it will be appreciated by those of ordinaryskill in the art that other dimensions of the PCB 18, strips 14 a, 14 band gap 16 are possible as well depending on a particular application aswill be described in detail below.

A high frequency signal generator 22 is electrically coupled to strip 14a and is operable to generate an electromagnetic field across thecoupling gap 16 that couples power to strip 14 b with the substrateplaced across, i.e., generally normal to the longitudinal axis of, thecoupling gap 16 in a packed manner as will be described in detail below.The signal generator 22 generates a coupled power signal in the coupledstrip 14 b that has an amplitude related to the impedance, and thereforethe moisture content, of the substrate placed across the coupling gap16. The signal generator 22 is phase locked to a crystal reference 24(FIG. 2A) to maintain frequency and therefore measurement accuracy,stability and repeatability and has an adjustable power 26. The signalgenerator 22 is preferably operable to generate signals in the VHF toUHF frequency ranges, i.e., between about 30 MHz and about 3 GHz,although other frequency ranges are possible as well. In accordance withone embodiment of the present invention, the signal generator 22 mayoperate at about 1 GHz, such as at about 915 MHz, since it iscontemplated that the water content of a substrate may be mostaccurately determined by its measured impedance in the near GHz range.

In accordance with one aspect of the present invention, the sensor 10utilizes the reverse power coupling variation of the high frequencydirectional coupler 12 to measure the change in the impedance of thematerial placed across the coupling gap 16. As the substrate is packedacross the coupling gap 16, the directional coupler 12 becomesmismatched, and this mismatch causes a monotonic increase in the reversepower coupling of the directional coupler 12 as the impedance across thegap 16 is increased as the result of increased moisture content of thematerial. The amplitude of the reversed power in the reflected power leg28 (FIGS. 1 and 2B) from strip 14 b is generally a direct measure of theimpedance, and hence the moisture content, of the substrate placedacross the coupling gap 16. As will be described in detail below, themoisture content of the substrate, i.e., its water content by weight,can be determined from the measured impedance of the sample.

Further referring to FIGS. 1 and 2A-2E, the forward power signal fromstrip 14 a is electrically coupled to one port of a mixer 30 through aforward power leg 32 (FIGS. 1 and 2B) and an attenuator 34. For example,the forward power signal may be attenuated to about −10 dBm by theattenuator 34. The coupled power signal from strip 14 b is phase shiftedby phase shifter 36 and is electrically coupled to another port of themixer 30 through the reflected power leg 28. The mixer 30 may act as acoherent receiver in that it is most responsive to coupled signals thatare in phase with the forward power signal. The phase shifter 36 assuresthe proper phase coherence of the reflected power signal relative to theforward power signal for the mixer 30 to produce the maximum discernablemixer output. With the mixer forward power set to the appropriate levelthrough the adjustable power 26, the output of the mixer 30monotonically increases with an increase in the reflected coupled power.The mixer 30 demodulates or reduces to DC base band the value of thecoupled power though the directional coupler 12. The DC output of themixer 30 is filtered and amplified by amplifier 38 to produce ameasurable output voltage that is related to the moisture content of thesubstrate placed across the gap 16. The amplifier 38 includes anadjustable gain 40 and an adjustable DC offset 42.

Referring now to FIGS. 4, 4A and 4B, use of the sensor 10 to determinethe moisture content of hair will now be described in connection with ahair moisture sensor system 44. Hair moisture sensor system 44 may beused by a professional salon, for example, to quickly, accurately andreliably indicate to a stylist when the moisture content of a customer'shair is in the range of approximately 30-40% by weight so that theoptimum styling results may then be achieved.

As shown in FIGS. 4A and 4B, a hair clamping device 46 is providedhaving pivoted jaws 48 and 50 that each terminate in a handle 52 thatmay be easily grasped and manipulated by the stylist. The jaws 48 and 50may be biased to an open position as shown in FIG. 4A so that a bundleof hair 54 is readily received between the jaws 48, 50 and is orientedwith the hair fibers 54 extending across, i.e., generally normal to thelongitudinal axis of, the coupling gap 16 of the directional coupler 12which is supported by jaw 50. As shown in FIG. 8, it has been determinedthat the packing pressure of C 5 the hair 54 across the coupling gap 16is important to ensure reliability in the moisture content measurement.With low packing density below about three (3) lbs., i.e., a packingdensity in the pressure region 56, the output voltage signal of themixer 30 may be unstable due to insufficient packing density of the hairfibers 54 across the coupling gap 16. At higher packing pressures aboveabout seven (7) lbs., i.e., a packing density in the pressure region 58,the output voltage signal of the mixer 30 begins to fluctuate as thehair fibers 54 will exhibit the result of difference in packing densityacross the coupling gap 16. At these higher pressures, excess moistureis also quickly expelled resulting in unreliable lower readings. It hasbeen determined that packing pressures in the range of about three (3)lbs. to about six (6) lbs., i.e., a packing pressure in the pressureregion 60, provides an output voltage signal from the mixer 30 that isstable to produce reliable and repeatable measurements of the moisturecontent.

In accordance with another aspect of the present invention, as shown inFIGS. 1, 2D, 4A and 4B, a pressure sensor 62 incorporating a filmpressure transducer 64, is supported by the jaw 48 in juxtaposition tothe directional coupler sensor 12. The pressure transducer 64 isoperable to generate an output voltage signal that varies with thepacking pressure applied to the hair 54 placed across the coupling gap16. As shown in FIGS. 1 and 2D, the output voltage signal from thepressure transducer 64 is amplified by amplifier 66 having an adjustablegain 68 and DC offset 70, and that amplified output voltage signal iseither provided directly at the output of the pressure sensor 62 throughjumper 72, or it is applied as an input to a comparator 74 throughjumper 76. A trigger voltage corresponding to a desired trigger pressureis set as a reference voltage 77 to the comparator 74. The measurementof the moisture content is triggered upon the crossing of the pre-setpressure threshold 77. This ensures that the desired compactness of thehair fibers 54 placed across the coupling gap 16 is achieved to obtainaccurate, reliable and repeatable results. It will be understood bythose of ordinary skill in the art that packing consistency can beachieved by a mechanical system (not shown) as well without departingfrom the spirit and scope of the present invention.

With reference to FIGS. 1 and 4, the measured signal from the sensor 10,and the trigger signal or pressure signal from the pressure sensor 62,are electrically coupled through a cable 78 to a processing system 80,such as a conventional PC or laptop computer. The processing system 80is operable to convert the measurement signal generated by the sensor 10into a moisture content value that may be presented on the display 82 ofthe system 80. As described in detail above, the measurement signal istriggered in response to the trigger signal generated by the pressuresensor 62. One or multiple measurements signals may be taken in responseto the trigger signal.

Referring now to FIGS. 6 and 7, the amplified output voltage of thesensor 10 is calibrated by first subjecting multiple switches of hair toa known moisture content via the use of relative humidity. The sensor 10is then used to generate a measurement signal for each switch of hair atthe various relative humidities, as shown in FIG. 6. Since hair exhibitsa generally linear relationship between moisture content by weight andrelative humidity as shown in FIG. 7, the processing system 80 isoperable to convert the amplified output voltage of the sensor 10 into avalue representing the moisture content by weight of the hair using alook-up table or algorithm. Since the water absorption capability ofdamaged hair and healthy hair will differ, the sensor 10 of the presentinvention may be used to provide a signal that is generally related tothe health of the hair. Generally, the health of hair is characterizedby such factors as smoothness, shine, absence of frigility, absence offissuring and absence of cuticular breakdown. As each of these factorsis directly or indirectly related to the moisture content of the hair,the sensor 10 of the present invention is able to provide an accurateand reliable indication of the health of measured in vivo or in vitrohair.

The sensor 10 of the present invention provides a consumer friendlyself-assessment tool that permits a consumer to periodically measure thegeneral health of the consumer's hair. Based on these measurements, theconsumer is able to take corrective actions as necessary which tend toimprove the health of the consumer's hair. These actions may includechanging hair care products, changing hair styling techniques, or both,so that the general health of the consumer's hair can be consistentlymonitored and improved. The sensor 10 also provides a useful monitoringtool to hair stylists and hair technicians as well.

In accordance with another aspect of the present invention, as shown inFIGS. 5A and 5B, the sensor 10 is incorporated into a hair care product,such as a brush 84, used for grooming hair. The brush 84 includes anelongated body portion 86 terminating in a handle 88. Bristles 90 extendin a conventional manner from the body portion 86 of the brush 84 toenable grooming of the hair. In accordance with the principles of thepresent invention, as shown in FIG. 3, the signal generator 22, mixer30, voltage regulator 92 (FIG. 2E) and electronics of the pressuresensor 62 are all integrated onto the PCB board 18 which is supported ona fixed base 94 of a hair clamping device 96 (FIGS. 5A and 5B). Thefixed base 94 positions the directional coupler 12 near the bristles 90so that measurements are easily taken while the hair is being brushed.The hair clamping device 96 includes a spring biased clamp member 98that positions the pressure transducer 64 in juxtaposition to thedirectional coupler 12. A lever 100 is operatively connected to themovable clamp member 98 to enable a user to clamp hair across thecoupling gap 16 when a sensor measurement is desired by moving the clampmember 98 toward the fixed base 94 as shown in FIG. 5B. The hair brush84 may include LED's, and/or produce an audible signal, to provide anindication to the user about the moisture condition, health or othercondition of the hair based on the sensor measurement. While not shown,in will be appreciated that the sensor 10 of the present invention maybe incorporated into other hair care products as well, such as a comb,curling iron, or similar hair care product that preferably engages theuser's hair during grooming to provide a measurement of the moisturecontent, health or other status of the hair based on the sensormeasurement.

The directional coupler sensor 10 of the present invention is wellsuited to measure the moisture content, health or other condition ofhair since it possesses sensitivity to variations in impedance in closeproximity, such as about 0.1 in., to the surfaces of the strips 14 a and14 b. The height of this effective measurement probing depth from thesurfaces of the strips 14 a, 14 b is a function of the electromagneticfield that couples the strips 14 a and 14 b. The height of themeasurement probing depth may be changed for a particular application bychanging the height of the PCB 18, the dielectric constant of the PCB18, the dimensions of the strips 14 a, 14 b, the coupling gap distance“s”, and/or the power supplied by the signal generator 22. By varyingany or all of these parameters, the height of the coupling field can bealtered to thereby change the effective measurement probing depth.

It is contemplated that sensor 10 may comprise multiple directionalcouplers 12 electrically coupled to at least one signal generator 22 tomeasure the respective moisture content of multiple substrates inaccordance with the principles described in detail above. It is furthercontemplated that at least two of the multiple directional couplers 12may have different effective measurement probing depths by varying oneor more of the parameters described in detail above.

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

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 9. A sensor for measuring healthof hair, comprising: a directional coupler having a pair of generallyparallel first and second strips defining a coupling gap therebetween;and a high frequency signal generator electrically coupled to said firststrip and operable to couple power to said second strip with the hairplaced across said coupling gap to thereby generate a coupled powersignal in said second strip having an amplitude related to health of thehair.
 10. The sensor of claim 9 wherein the amplitude of said coupledpower signal is related to moisture content of the hair.
 11. The sensorof claim 9 wherein the amplitude of said coupled power signal is relatedto smoothness of the hair.
 12. The sensor of claim 9 wherein theamplitude of said coupled power signal is related to shine of said hair.13. The sensor of claim 9 wherein the amplitude of said coupled powersignal is related to absence of frigility of the hair.
 14. The sensor ofclaim 9 wherein the amplitude of said coupled power signal is related toabsence of fissuring of the hair.
 15. The sensor of claim 9 wherein theamplitude of said coupled power signal is related to absence ofcuticular breakdown of the hair.
 16. The sensor of claim 9 furthercomprising a hair clamping device supporting said directional couplerand said high frequency signal generator, said clamping device beingoperable to apply a packing pressure to the hair across said couplinggap.
 17. The sensor of claim 16 further comprising a pressure sensorsupported by said hair clamping device and operable to generate a signalrelated to the packing pressure applied by said hair clamping device tothe hair.
 18. The sensor of claim 17 wherein said hair clamping devicecomprises a pair of pivoted jaws each terminating at a remote endthereof in a handle, wherein said directional coupler is supported byone of said jaws and said pressure sensor is supported by said other jawin juxtaposition to said directional coupler.
 19. The sensor of claim 9wherein said high frequency signal generator is operable to generate aforward power signal in said first strip and a reverse power signal insaid second strip.
 20. The sensor of claim 19 further comprising a mixercircuit electrically coupled to said first and second strips andoperable to receive said forward power signal from said first strip andsaid reverse power signal from said second strip to thereby generate anoutput voltage signal having a value related to health of the hair. 21.A hair care appliance for use in grooming hair, comprising: an elongatedbody portion terminating in a handle; at least one hair styling membersupported by said elongated body portion and operable to engage the hairto effect the grooming thereof; a directional coupler supported adjacentsaid hair styling member and having a pair of generally parallel firstand second strips defining a coupling gap therebetween; and a highfrequency signal generator electrically coupled to said first strip andoperable to couple power to said second strip with the hair placedacross said coupling gap to thereby generate a coupled power signal insaid second strip having an amplitude related to health of the hair. 22.The sensor of claim 21 wherein the amplitude of said coupled powersignal is related to moisture content of the hair.
 23. The sensor ofclaim 21 wherein the amplitude of said coupled power signal is relatedto smoothness of the hair.
 24. The sensor of claim 21 wherein theamplitude of said coupled power signal is related to shine of said hair.25. The sensor of claim 21 wherein the amplitude of said coupled powersignal is related to absence of frigility of the hair.
 26. The sensor ofclaim 21 wherein the amplitude of said coupled power signal is relatedto absence of fissuring of the hair.
 27. The sensor of claim 21 whereinthe amplitude of said coupled power signal is related to absence ofcuticular breakdown of the hair.
 28. The sensor of claim 21 furthercomprising a hair clamping device associated with said elongated bodyportion and supporting said directional coupler, said clamping devicebeing operable to apply a packing pressure to the hair across saidcoupling gap.
 29. The sensor of claim 28 further comprising a pressuresensor supported by said hair clamping device and operable to generate asignal related to the packing pressure applied by said hair clampingdevice to the hair.
 30. The sensor of claim 29 wherein said hairclamping device comprises a fixed base member supporting saiddirectional coupler and a movable clamp member supporting said pressuresensor in juxtaposition to said directional coupler.
 31. The sensor ofclaim 21 wherein said high frequency signal generator is operable togenerate a forward power signal in said first strip and a reverse powersignal in said second strip.
 32. The sensor of claim 31 furthercomprising a mixer circuit electrically coupled to said first and secondstrips and operable to receive said forward power signal from said firststrip and said reverse power signal from said second strip to therebygenerate an output voltage signal having a value related to health ofthe hair.
 33. A method for measuring moisture content of a substrate,comprising: generating an electromagnetic field through the substrate;measuring the reactance of the substrate in response to theelectromagnetic field; and determining the moisture content of thesubstrate from the measured reactance.
 34. The method of claim 33wherein the electromagnetic field is generated by a high frequencysignal source electrically coupled to a directional coupler having apair of generally parallel first and second strips defining a couplinggap therebetween.
 35. The method of claim 34 wherein the substrate isplaced across the coupling gap.
 36. The method of claim 34 wherein thehigh frequency signal source operates in the RF frequency range.
 37. Themethod of claim 34 wherein the high frequency signal source operates inthe microwave frequency range.